We propose to perform planning and development of a proton medical facility to be located at the Massachusetts General Hospital, with the goal of completing the facility In approximately five years time. The facility would be used for proton therapy research and treatment of inoperable and inaccessible tumors located in and around the brain, as well as other appropriate malignancies. The facility as conceived at present will have two treatment stations with isocentric gantries capable of delivering a treatment beam from any angle and thus suitable for a wide range of treatments, and a fixed beam treatment station suitable for treatment of ocular tumors and intracranial lesions. Proton radiation treatments delivered at the Harvard Cyclotron Laboratory by a collaboration of Massachusetts General Hospital, Harvard Cyclotron Laboratory, and Massachusetts Eye and Ear Infirmary personnel, as well as at other centers around the world, have yielded evidence of significant clinical gains achievable with this cancer treatment modality. The construction of a hospital based proton medical facility will increase the availability of proton treatments for proven therapies and expand the capability to conduct research into areas of promise for proton treatments of cancer. We propose to explore the worldwide experiences in proton therapy and analyze these for implications for the structuring of a new facility. We would review the existing technologies pertinent to proton therapy and analyze them with regard to their adequacy and to the possibility of improving their design. Additionally we would explore alternative new technologies and analyze them with regard to possible technical advantages of the new designs and their potential for reducing the cost of the facility. The specific items to be considered in these studies include the proton accelerator, beam transport system, beam delivery system, and control and monitoring systems. We would also undertake architectural and engineering studies, of the physical facility and available sites to analyze the site specific requirements, including radiation safety shielding, utilities requirements, construction techniques, and facility integration into the hospital infrastructure. Additionally we propose to explore the financial viability of the facility with respect to probable patient volume, capacity for research activities, and staffing and other operating requirements.